Determinations of crystalline structure and molecular sterochemistry for selected metalloporphyrins are in progress and in prospect. Three-dimensional X-ray data, recorded on a computer-controlled four-circle diffractometer, are employed in the analyses of structure. Six-coordinate iron(II) derivatives of the "picket fence" porphyrin, meso-tetra alpha, alpha, alpha, alpha,-o-pivalamidephenyl) porphine command the highest interest. Crystals of two six-coordinate species that have carbon monoxide as one axial ligand of the iron atom and N-methylimidazole or N-n-butylimidazole, respectively, as the other are under study. Structure analysis for crystals in which the molecular ratio of tetrahydrofuran (THF) to meso-tetraphenyl-porphinatoiron(II) is 2:1 also is in prospect. The magnetic suscAptibility of these crystal at room temperature correspons fully to high-spin iron(II)